The present invention concerns a rear suspension for a vehicle such as a bicycle, motorcycle or similar, of the type comprising a chassis, hereafter called an underframe, a swing arm integral with the underframe and bearing the hub axle of a rear drive wheel, and a shock absorber whose ends are respectively integral with the underframe and swing arm, said suspension providing an xe2x80x9canti-bobbingxe2x80x9d effect and leaving clear the space between the seat and rear wheel to allow the fixation of a mud guard, carrier rack or similar.
In the area of mountain-biking, called MTB, rear suspensions are well known comprising a swing arm articulated in the lower part of the seat tube cooperating with a shock absorber. This is the case, for example, with the xe2x80x9cXC FULLxe2x80x9d bike marketed by LAPIERRE; the swing arm pivots around a fixed axle parallel to the axle of the engaging sprocket which is borne by the crankset positioned at the intersection between the down tube and the seat tube. In addition, the ends of the shock absorber are integral with the swing arm and respectively with the top tube connecting the seat tube to the bicycle fork or an intermediate tube extending globally from the crankset to the top tube, said seat tube being non-continuous to allow passage of the shock absorber.
This type of rear suspension has the disadvantage of taking up the space at the rear of the bicycle, i.e. the space between the rear wheel and the seat, so that it is impossible to fix a rear mudguard, being the cause therefore of various projections of mud, water, etc. onto the cyclist""s back in the event of rain for example. Also, in the event of sudden fast pedalling, such as cranking to pick up speed or if the cyclist stands on the pedals when climbing a hill etc., this type of rear suspension gives rise to a so-called xe2x80x9cbobbing effectxe2x80x9d leading to cyclic bouncing of the suspension even on level ground. Therefore, in addition to the cycling discomfort this causes, part of the torque drive provided by the cyclist is dispersed in the shock absorber instead of contributing to the momentum of the bicycle.
With this type of rear suspension, the upper tensioned strand of the transmission chain extending between the engaging sprocket, borne by the crankset, and the engaged sprocket, integral with the rear drive wheel, extends above the rotation axle of the swing arm relative to the underframe thereby setting up a torque proportional to the tension of the upper strand and at a distance which separates the upper strand of the chain from the centre of rotation of the swing arm, which tends to cause the swing arm to pivot upwards thereby compressing the shock absorber when the cyclist pushes on the pedals, the bicycle being in static equilibrium, i.e. when mounted by a cyclist. When the torque drive applied to the pedals by the cyclist is relatively low and constant, the drive applied to the swing arm and consequently the downward movement of the shock absorber are equally small and constant, so that the cyclist does not perceive any bobbing effect even though part of the torque drive is dispersed within the shock absorber, thereby reducing the efficacy of pedalling. However, when the cyclist pedals harder or when the cyclist stands on the pedals to pick up speed, the position of the centre of gravity of the bicycle/cyclist pair varies; this causes a vertical oscillating movement of the bicycle frame so that the torque drive is suddenly increased, causing an increase in the drive applied to the swing arm which compresses the shock absorber and gives rise to the bobbing effect rapidly perceived by the cyclist. Therefore when pedalling energetically there is a strong increase in the torque drive which becomes cyclical and with each pedal movement it increases the drive applied to the swing arm which compresses the shock absorber giving rise to a bobbing effect, the latter being characterized by a parasitic alternate compression movement of the bicycle""s front and rear suspensions in rhythm with the rate of pedalling which hampers the cyclist.
To overcome this disadvantage, a bicycle rear suspension has already been imagined which provides a so-called xe2x80x9canti-bobbingxe2x80x9d effect; this is the case for example in French patent FR 2.774.966 filed by the Applicant describing a rear bicycle suspension comprising a swing arm guided by two connecting rods. The orientation of the two rods is set such that the intersection of their respective axes passing through the centre of their two pivots, said intersection materializing the instantaneous centre of rotation of said swing arm, is positioned in the upper anterior quadrant of the point defined by a horizontal axis and a vertical axis converging towards the centre of the crankset, and are articulated on said swing arm at two points notably distant from one another. The suspension also comprises a shock absorber whose ends are respectively integral with the swing arm and the seat tube, said shock absorber extending globally parallel to said seat tube at its rear.
Even though this type of suspension provides an anti-bobbing effect, it has the disadvantage of taking up space at the rear of the bicycle so that it is not possible to fix a rear mudguard, carrier rack or similar. Also, even though this type of suspension provides a particularly effective anti-bobbing effect, it nevertheless has the disadvantage of imparting insufficient rigidity to the underframe/suspension assembly which, when intensive demand is placed on the bicycle, is detrimental to the general performance of the bicycle making it uncomfortable.
One of the purposes of the invention is therefore to overcome these disadvantages by putting forward a rear suspension for a bicycle, or similar, formed of a swing arm connecting the axle of the rear wheel to the upright of the underframe, and a shock absorber whose ends are integral with the underframe and swing arm respectively, said underframe and/or swing arm comprising means making it possible to clear the space between the seat and rear wheel to allow fixation of a rear mudguard or a carrier rack for example, while providing an anti-bobbing effect.
For this purpose, the invention provides for an anti-bobbing system of the rear suspension of a vehicle, such as a bicycle, motorcycle or similar, of the type comprising an underframe, swing arm integral with the underframe bearing the hub axle of a drive wheel, and a shock absorber whose ends are respectively integral with the underframe and swing arm, the torque drive being transmitted to the drive wheel via a chain extending between an engaging sprocket integral with the underframe and an engaged sprocket integral with the hub axle of the drive wheel, said chain between the engaging and engaged sprockets forming two strands, an upper tensioned strand transmitting the torque drive to the drive wheel and a lower so-called return strand, the underframe formed of a globally vertical seat tube, a top tube and a down tube, the top tube and the down tube being integral with a head or steering tube bearing a fork, the axle of the engaging sprocket being positioned at the intersection of the seat tube and down tube and/or the swing arm comprising means so that the upper strand of the transmission chain or the straight line extending it passes through the instantaneous centre of rotation C of the swing arm when the vehicle is in a position of static equilibrium and so that said upper strand of the chain is located below the instantaneous centre of C of the swing arm when the hub of the drive wheel is located above its reference position Pr corresponding to the position of the hub axle of the drive wheel when the vehicle is in a position of static equilibrium. The rear suspension is remarkable in that the swing arm is made integral via at least two articulation means with the underframe whose intersection of the straight lines D1, D2 passing through the rotation axles of each articulation means is positioned in the upper posterior quadrant of a point defined by a horizontal axis H and a vertical axis V converging towards to the axle of the engaging sprocket and in that the ends of the shock absorber are respectively integral with the swing arm or the articulation means joining the swing arm to the down tube, and with a hanger of the down tube, said hanger extending along the plane containing the underframe tubes, said shock absorber extending in front of the down tube i.e. between the down tube and the fork bearing the front wheel, globally parallel to the latter or between the tubes forming the underframe in the plane containing the latter.
It is can be easily understood that when the vehicle is ridden over perfectly level ground, the upper strand of the transmission chain passing through the instantaneous rotation centre of the swing arm, i.e. the rotation centre of the swing arm at each time t, the entirety of the torque drive is transmitted to the drive wheel, and that when the cyclist changes rhythm and pedals harder for example the upper strand of the chain being located below the instantaneous rotation centre of the swing arm, a restoring moment is set up proportional to the tension of the upper strand of the chain and at a distance separating the upper strand and the instantaneous centre of rotation of the swing arm, which tends to return the swing arm to its initial position. This restoring moment is set up whenever the cyclist pedals harder, thereby avoiding the onset of the bobbing effect. Obviously, when overcoming an obstacle, the restoring moment adds itself to the restoring force of the shock absorber, considerably improving motive power when climbing hills for example. Also, unlike the teaching of French patent FR 2.774.966 in which the instantaneous centre of rotation of the swing arm is located in the upper anterior quadrant of the bicycle, the position of the instantaneous centre of rotation is located in the upper posterior quadrant and the position of the shock absorber on the down tube of the bicycle imparts greater rigidity to the underframe/suspension assembly making it possible to clear the space between the rear wheel and the seat so as to fix a rear mudguard, carrier rack or similar.
According to one particularly advantageous characteristic of the rear suspension of the invention, the instantaneous centre of rotation of the swing arm moves globally along a straight line perpendicular to the upper strand of the chain when the hub axle of the drive wheel moves, so that the restoring moment is proportional to the movement of the hub axle of the drive wheel.